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Rudder Cable Link lengths, rigging

woodsideraff

Well Known Member
I am ready to mark and drill the rudder cable links. If I increase the cable tension enough, I end up with practically no length for the links.

I was pretty careful in building my wooden rigging fixture, using high quality 1/2" plywood instead of the crating wood. I'll check again the dimensions tomorrow when I return to the airport to build.

I'm wondering what is the link length that others end up with?

How much tension should be put on the cables for drilling?

Anybody with a good idea on clamping the rudder exactly on trail?

Also, it seems to me that, since the rudder pedal cable attach points are higher than the back bulkhead bushings, there will be quite a bit of rubbing on the top side of the bushings in the most forward bulkhead. How long before that cable eats through the bushing?

It's been my experience that whenever something doesn't fit perfectly, I've done something wrong. Hope this is the case again this time.

Cheers,

Rafael

RV8A bought and flying

RV12 500 hours into the build
 
32-12 Rudder links

See my hints:
http://www.vansairforce.com/community/showthread.php?t=70542
When completed, the center of the holes were exactly 2" apart on the left link and 1" apart on the right link.
The rudder cable lengths are not critical. When flying, your feet keep the cables tight. Otherwise the cables sag and touch the tail cone frames. Your feet will not be able to tell if a cable is a little bit too short or too long.
How much tension should be put on the cables for drilling?
Not enough to bend anything. Just pull the cable tight by hand and mark.
If I increase the cable tension enough, I end up with practically no length for the links.
Something is wrong.
Joe Gores
 
The rudder cable lengths are not critical. When flying, your feet keep the cables tight.

Not entirely true.

If the links are too long the rudder pedals will be bumping the firewall when the rudder hits the travel stops. If the links are excessively long, you will never get full rudder travel before the rudder pedals get stopped by the firewall.
 
Rudder pedal rigging and cable lengths

1- I have my pedal assy located per plans (even though I drilled for two more positions). Also noting that if this position changes, so will the cable length.

2- I used a length of 1" angle zip tied around the lower petal beams to keep all aligned. In doing so, this also 'locks' the forward/aft movement/position of the pedals- Note- This is the ONLY way to get 'tension' in the cables. Without restraining all pedals, there will be no tension.

3- I use a length of 6-32 threaded rod and fender washers slipped through the counterbalance gap at the top of the rudder/vertical to hold the rudder at neutral (and also the elevators/horizontal).

4- In doing all this, my lengths are longer than expected- 3.1" & 3.5" hole to hole.

5- As mentioned, the actual lengths are not that critical, but need to make sure the rudder pedals don’t hit the firewall at full travel. I am only repeating this because you also need to consider include brake petals as well.

6- Going back to point 4, although I am happy with the rigging, one issue I had given the length of the links, the swedged end of the cable actually snags on the first guide hole. Still working a solution for this.
 
I bought my RV12 so I didn't build it, mine has a pretty large wedge attached to the LH side of the rudder as a tab...I'm not sure that when the holes were drilled the rudder was neutral... I don't understand why cable turn barrels are nut used in the rudder system like they are in the horz. stab. this way you could rig the rudder to a closer tolerance than by drilling holes...also the cables when slack rest on one of the fuselage formers, I applied a few layers of aluminum tape to keep them from getting worn.
 
1- I have my pedal assy located per plans (even though I drilled for two more positions). Also noting that if this position changes, so will the cable length.

2- I used a length of 1" angle zip tied around the lower petal beams to keep all aligned. In doing so, this also 'locks' the forward/aft movement/position of the pedals- Note- This is the ONLY way to get 'tension' in the cables. Without restraining all pedals, there will be no tension.

3- I use a length of 6-32 threaded rod and fender washers slipped through the counterbalance gap at the top of the rudder/vertical to hold the rudder at neutral (and also the elevators/horizontal).

4- In doing all this, my lengths are longer than expected- 3.1" & 3.5" hole to hole.

5- As mentioned, the actual lengths are not that critical, but need to make sure the rudder pedals don’t hit the firewall at full travel. I am only repeating this because you also need to consider include brake petals as well.

6- Going back to point 4, although I am happy with the rigging, one issue I had given the length of the links, the swedged end of the cable actually snags on the first guide hole. Still working a solution for this.

Are you building an RV-12? That is what this conversation was about ( the 12 is a little bit different from the others.
 
The holes in rudder cable links could be a half inch off and it would not have any affect on rudder trim. The length of the rudder cables does not affect rudder trim.
I don't understand why cable turn barrels are not used in the rudder system like they are in the horz. stab. this way you could rig the rudder to a closer tolerance than by drilling holes.
 
I believe what your saying but it doesn't make sense to me, most of all my GA experience is Cessna and Piper.
 
When you fly the plane and determine that rudder trim is necessary to center-the-ball you will add the triangular metal tab to the trailing edge of the rudder. This will aerodynamically bias the rudder and eliminate the need to hold rudder pressure with your feet ? thus it doesn?t matter if the rudder cables are not equal length. The rudder trim tab should be bent at an angle to allow the airplane to fly straight (no skid or slip) in cruise flight. You will still need to hold a significant amount of right rudder in a climb to overcome engine torque and P-factor.
 
Or just rivet on a conventional trim tab after certification like I did. I also put them on the flaperons. Old school, but makes adjustments easy.
 
I believe what your saying but it doesn't make sense to me, most of all my GA experience is Cessna and Piper.

Good Morning Bob,

If you think about it this way, it is easier to understand what the others are saying.

As long as you are not applying any pressure to one rudder pedal or another, the rudder will center aerodynamically in flight. That is why to change the trim on an RV-12 rudder a wedge or trim tab is required. The cable length does not come into play.

But, the cables including the links do need to be of the correct length so that the pedals are in the same positions when the rudder is centered, and they do not contact the firewall when fully deflected. That is why Van?s has the builder construct a simple wooden jig to use when doing the final fit of the cables.

If you are unsure of the rigging in the airplane you purchased, you could check this out by clamping the rudder in the center, and running staright edge across the pedals with them gently pushed forward. They should be equally deflected. Then remove the clamp and check full defelction of each pedal to be sure neither one contacts the firewall.

Hope this helps,

John
 
Not entirely true.

If the links are too long the rudder pedals will be bumping the firewall when the rudder hits the travel stops. If the links are excessively long, you will never get full rudder travel before the rudder pedals get stopped by the firewall.

And, the cables dont have to be very much too long to hit the firewall. When I built my 12 I didnt leave enough clearance between the fully deflected rudders and the firewall, even though the rudder itself was hitting the stops. After a couple of years I noticed these little bumps appearing on the front side of the firewall. (The firewall material is pretty soft.)
 
I'm familiar with metal tabs, but when rigging I would set neutral to either pedals or control wheel/stick with a straight edge and clamps, then adjust the flight control to neutral using cable adjustments. If a tab was needed it wouldn't take much input/bend...My RV12 as a hefty wedge on the LH side of rudder and in level flight the ball is still off to the right a little. With the pedals in neutral the rudder TE is slightly to the left. I figured if I had cable turn barrels
I could adjust it more to center and possibly install a smaller tab.
 
I'm familiar with metal tabs, but when rigging I would set neutral to either pedals or control wheel/stick with a straight edge and clamps, then adjust the flight control to neutral using cable adjustments. If a tab was needed it wouldn't take much input/bend...My RV12 as a hefty wedge on the LH side of rudder and in level flight the ball is still off to the right a little. With the pedals in neutral the rudder TE is slightly to the left. I figured if I had cable turn barrels
I could adjust it more to center and possibly install a smaller tab.

You might consider removing the wedge and installing the Van's rudder trim tab available as a retrofit kit. Search the web store for "12 Rudder Trim Kit". It costs only 7 bucks.
 
I'm familiar with metal tabs, but when rigging I would set neutral to either pedals or control wheel/stick with a straight edge and clamps, then adjust the flight control to neutral using cable adjustments. If a tab was needed it wouldn't take much input/bend...My RV12 as a hefty wedge on the LH side of rudder and in level flight the ball is still off to the right a little. With the pedals in neutral the rudder TE is slightly to the left. I figured if I had cable turn barrels
I could adjust it more to center and possibly install a smaller tab.

As John already tried to explain, the rigging of the rudder cable lengths has no bearing on whether an RV-12 flys with the slip/skid ball centered. The purpose of any trim tab (rudder or others) is to induce a trimming force when there is no pilot force induced into the control circuit.

The whole purpose of a trim tab is to make the airplane fly in trim so that the pilot doesn't have to constantly hold some control presssure for it to do so.
The RV-12 rudder pedals move relatively freely. With no foot pressure on the pedals, the rudder will move to it?s aerodynamically balanced position. If that position happens to be with the ball displaced (out of trim) the rudder pedals will move where ever the rudder moves them (via the cables).

The only way rudder cable length would change yaw trim is if in straight and level flight the pilot always kept his feet on the rudder pedals with the pedals centered. That would be an airplane that was not considered to properly fly in trim.
Possibly your concern is that if an aerodynamic trim tab is holding the rudder deflected, that in level flight the rudder pedals are then no longer aligned. This doesn?t seem important and pilots don?t notice because it is generally a very small displacement. What is most important is that when the pedals are aligned, that the pilot knows that the rudder is centered / neutral.
 
Thanks guys, that makes sense now...the rudder will fare aerodynamically, the tab will work to center the ball.
 
BTW, when I received the factory trim tab plate it was pre-bent. When installed it perfectly centered the ball and there was no need to tweak it.
 
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